The notion of economics being a ‘moral science’ is far older than Keynes.
In his <href="http://www.econlib.org/library/Mill/mlUQP5.html&quot; title=Essays on Some Unsettled Questions of Political Economy Mills defined economics as a moral science, in direct opposition to the physical sciences. (This is also, of course, the essay in which Mill comes to define political economy as “The science relating to the moral or psychological laws of the production and distribution of wealth.”)
The philosophical justifications for Mill’s ‘moral’ definition of political economy are too often ignored. Mill comes to this conclusion through serious reflection on the nature of ‘science.’ His conclusion was that either 1) economics is a moral science, or not a science at all. - crookedtimber.org